In the presense of a block being initialized, the frontend will emit the
objc_retain on the original pointer and the release on the pointer loaded from
the alloca. The optimizer will through the provenance analysis realize that the
two are related (albiet different), but since we only require KnownSafe in one
direction, will match the inner retain on the original pointer with the guard
release on the original pointer. This is fixed by ensuring that in the presense
of allocas we only unconditionally remove pointers if both our retain and our
release are KnownSafe (i.e. we are KnownSafe in both directions) since we must
deal with the possibility that the frontend will emit what (to the optimizer)
appears to be unbalanced retain/releases.
An example of the miscompile is:
%A = alloca
retain(%x)
retain(%x) <--- Inner Retain
store %x, %A
%y = load %A
... DO STUFF ...
release(%y)
call void @use(%x)
release(%x) <--- Guarding Release
getting optimized to:
%A = alloca
retain(%x)
store %x, %A
%y = load %A
... DO STUFF ...
release(%y)
call void @use(%x)
rdar://13750319
llvm-svn: 181743
Michael Gottesman